Various types of attachments have been used to hold the case of a wrist instrument or timepiece on the wrist of the wearer, such as expansion bands, link bracelets and flexible straps. A popular type of attachment is a strap consisting of two strap halves each of which are attached to lugs on the case of the wrist instrument at one end and which are then buckled together on the other ends. Buckles for watch straps are well known in the art. Ordinarily, one end of the strap is folded around a transverse member on the buckle frame and secured, the transversed member also pivotally supporting the tongue of the buckle which extends through a hole in the strap. The end of the other strap half contains a number of adjustment holes. This end of the strap is inserted beneath another transverse member and the pivotal tongue of the buckle inserted through one of the holes. Then the free end or tongue of the strap is either inserted into a keeper loop on the strap or in some cases beneath a keeper bar on the buckle.
One of the disadvantages with a conventional buckle attachment is that the buckle must be fabricated separately, usually of metal and then attached to a strap. The free end of the strap or tongue then is preferably held against the strap by a keeper loop. However, the end of the strap which extends beyond the keeper loop tends to catch on things. Using a keeper loop also requires an extra piece and more assembly, all of the above adding to the cost of the watch attachment. If spring bars are employed, the extra material and time to attach the strap to the watch case using the spring bars also add to the cost of the attachment.
Suggestions have been made for using a single strap instead two strap halves and molding the central part of the plastic strap around projections or integral protrusions on the watch case, as in the case of U.S. Pat. No. 4,462,697 issued Jul. 30, 1984 to H. B. Thompson and assigned to the present assignee, or utilizing a pre-formed hard plastic annular insert overmolded with a soft plastic strap material as shown in U.S. Pat. No. 4,178,751 issued Dec. 18, 1979 to Liautaud. The latter patent also utilizes a plastic clasp, wherein the tongue of the watch strap is inserted into a channel-shaped "keeper" enclosure on the other strap half and the length of the strap adjusted by means of lateral opposed ridges and serrations on the mating portions on the strap halves. However, the use of a channel or sheath to act as the keeper, requires extra material.
Improvements in battery life, particularly with the use of lithium energy cells, have made feasible the concept of a disposable wristwatch with a sealed case using a long life energy cell and low cost components so that the wristwatch may be discarded at the end of the battery life. This means that the conventional removable case back to replace the energy cell is no longer necessary and the case of the watch or wrist instrument may be permanently sealed. The need to utilize very low cost components has lead to the search for a strap attachment which does not require a separate buckle and keeper loop.
Accordingly, one object of the invention is to provide an improved strap attachment for a low cost wristwatch.
Another object of the present invention is to provide an improved strap attachment which does not require a separate buckle member.
Another object of the invention is to provide an improved "keeper" for the free end of the strap so it will not catch on anything.
Another object of the present invention is to provide a low cost strap attachment which is suitable for a sealed timepiece case.